Studies are being conducted on the mechanical behavior of ischemic myocardium in experimental canine myocardial infarction. Aneurysmal bulging of ischemic segments of myocardium is being studied, both with reference to changes which occur naturally over a period of time, and with reference to the way in which this is influenced by various interventions. Both anesthetized open-chest (acute) and intact conscious (chronic) preparations, are being investigated, the latter using both angiographic methods, and methods for radiographically outlining the ischemic segment (implanted metallic beads). Interventions being tested include exercise, hypoxia, acidosis, and injections of cardiac- stimulating and depressing agents such as isoproterenol and propranolol. These interventions have the potential for both increasing or decreasing the degree of ischemic myocardial damage, and it is hoped that the methodology employed may provide information indicating whether the net effect upon ischemic myocardium is beneficial or detrimental. In addition, studies are being carried out on the effects of anoxia, hypoxia and ischemia in isolated perfused rat hearts, and of metabolic factors controlling cardiac output in intact animals.